1. Technical Field
This invention relates to apparatus and methods for seal or leak testing flexible packages such as plastic bottles.
2. Background Art
The prior art includes a variety of apparatus and methods for detecting defective seals or detecting leaks in containers.
In particular, U.S. Pat. No. 4,587,619 (issued May 6, 1986 to Converse et al.) discloses a complex microprocessor controlled leak detector wherein pressure readings within the container are taken at predetermined time intervals for determining the rate of change of pressure within the container.
The prior art also includes U.S. Pat. No. 4,511,044 (issued Apr. 16, 1985 to Connor et al.) which discloses the use of a force-applying member for securing a seal to a container and a sensor on the force-applying member that generates a signal corresponding to the applied force for use by a discrete logic system or a microprocessor-control system for comparing the force to a reference. This system is readily distinguishable from the invention, particularly in that the resistance of the container itself to an applied force or pressure is not sensed; rather, it is only the force applied to the seal member that is measured.
The prior art also includes several references each directed to detecting leaky packages by applying pressure to a flexible wall of the package and sensing if the internal pressure is capable of resisting the force.
For example, U.S. Pat. No. 4,517,827 issued May 21, 1985 to Tapscott) shows apparatus for conducting testing of multiple containers in a package by inserting probes through openings in the outer package which contact the individual flexible packages within the container to determine their hardness or ability to resist deformation. U.S. Pat. No. 4,148,213 (issued Apr. 10, 1979 to Prakken) simply applies conveyor belt forces to a flexible package and removes soft packages from between the conveyor belts by an air stream. U.S. Pat. No. 4,510,730 (issued Apr. 16, 1985 to Edmondson) compresses a flexible package between pressure members and detects if the pressure members have been closed by more than a predetermined amount, indicative of a fully sealed or non-sealed container.
In U.S. Pat. No. 3,837,215 (issued Sep. 24, 1974 to Massage) a leak rate of a sealed container is determined by placing the container within a sealed test chamber and changing the pressure within the chamber over a time period. A first measurement is taken of a physical dimension of the container at the end of the first time period to produce a first signal and the same physical dimension is again measured at the end of a second time period to produce a second signal indicative of any change of the physical dimension. Any difference between the first and second output signals produces a third signal indicative of a leak rate of the container. The U.S. Pat. No. 3,751,972 (issued Aug. 14, 1975 to Hass) teaches a process and apparatus for batch testing of sealed containers by measuring physical dimensions of the container before and after it has been pressurized. The signal obtained after the container has been pressurized is measured after a predetermined time interval has elapsed after the pressure has been applied to the container.
In German OS No. 2422526 of P. Kallenowski, plastic bottles are compressed between two converging belts. At the point of minimum gap between the belts, a pressure measuring device senses the pressure within the bottles and emits a pulse when a pressure is out of acceptable range. However, it would not appear that a series of pressure readings is taken at predetermined time intervals to determine the general slope of a pressure-time curve characteristic of the ability of a pressurized container to react to an applied load.
Notwithstanding the numerous efforts of the prior art, there remains a continuing need for new and useful apparatus and methods for measuring reliably for the existence of leaks in flexible, sealed containers.